Granulation of fusible, molecularly orientable polymers



May 13, 1958 F. BILANIN ETAL.

GRANULATION OF FUSIBLE, MOLECULARLY ORIENTABLE POLYMERS Filed Nov. 4,1955 m; mdmIjOd muuu mFDIU .Noi v w .tkm m m93@ oziuzmaa INVENTORS;FRANK BILANIN,

HARRY EGRONICH,

BYMJCQM VATTORNEY GRANULATIN F FUSIBLE, MOLECULARLY ORIENTBLE POLYMERSFrank Bilanin, Morris Plains, Harry E. Gronich, deceased, iate ofMorristown, by Claire K. Gronich, Morristown, N. l., legalrepresentative, assignors to Allied Chemical & Dye Corporation, NewYork, N. Y., a corporation of New York Application November 4, 1955,Serial No. 545,046

4 Claims. (Cl. 18-47.5)

This invention relates to conversion of a fusible, molecularlyorientable polymer into granules suitable for use as molding powder, asstarting material for a melt spinning process, etc. The process isapplicable generally to polymers having the physical properties of beingfusible in substantially pure condition, being extrudable from the melt,having a crystalline or micro-crystallinecharacter and being moleculariyorientable upon stretching.

lt has been proposed to convert such polymers into chips for use in meltspinning processes by extrudng a strip of polymer from the melt, coolingthe strip and cutting the strip into suitably sized squares by use of apunch press. in this proposed process the strip must be kept cool enoughto prevent stickiness and at the same time kept hot enough to reduceirregular breakage and shattering which result in nonuniformity and nes.

The present inventors have discovered and developed a process forgranulation of fusible, molecularly orientable organic polymers whichallows cutting very uniform granules over a wide temperature rangewithout producing nes such as result from brittleness of the polymer cutby the above cited process. This new process permits high productionrates and permits utilization of a high speed rotary cutter.

In' the new process molten -organic polymer is extruded as separate,rounded, essentially uniform, essentially nonmolecularly-orientedfilaments into water or like inert liquid. Then the submerged filamentsare gathered into side by side contact in one or more banks, forming aribbon, while still at average temperature in the plastic range asdefined below but not until the filament surface has cooled beiow theweld temperature, i. e. the temperature at which fusion occurs andcoalescence between filaments will develop immediately at all adjacentareas.

The cooling liquid extracts heat from the exposed surfaces of theresulting ribbon of filaments so as to keep at least the major portionof these exposed surfaces below the weld temperature; but heat flow fromthe cores of the individual filaments brings their laterally contactingsurfaces into the plastic range of temperature, i. e. in the temperaturerange in which measurable permanent deformation of the polymer surfacewill occur under the pressure being exerted laterally to gather theextruded filaments, within the time in which the filaments are held incontact before being cut.

Travel through the cooling liquid is continued at least until the ribbonhas solidified into a connected structure, preferably until temperatureat the points of contact of the lame'nts has been reduced below theplastic range. Preferably the average temperature remains above theboiling point of the cooling liquid which will then evaporate off fromthe finished granules.

Thereby a lateral bond is formed at points of contact between theindividual filaments, having a strength which depends upon the averagetemperature `of the filaments at the time they are brought into contact(and thus upon the quench between extrusion and gathering); upon l2,834,053* Patented May 13, 1958 the lateral pressure exerted ingathering the filaments; and upon the time of contact of the filamentswhile in the plastic range of temperature.

The resulting filament ribbon is drawn through the nip of a pair of feedrolls, and the advancing end of fthe ribbon is severed by a cutterpreferably with a slicing action, e. g. by a high speed rotary cutter.The speed of the feed rolls should be coordinated with the rate offilament extrusion so that no tension develops sufficient tosubstantially molecularly orient the filaments by stretching Unorientedfilaments cut and break apart better than roriented filaments; henceyorientation is avoided.

The stroke of the cutter breaks the lateral bonds between individualfilaments beyond the cutting block at the same time as it cuts themtransversely, thereby forming granules. Because the filaments adherelaterally at least until they pass through the feed rolls, the problemof uneven feed of individual filaments to the cutter is solved.

It is not necessary that all the filaments adhere laterally throughoutthe full length of the ribbon emerging from the cooling bath; it is onlynecessary that lateral bonds occur at such intervals that the ribbonmaintains its integrity until it passes through the feed rolls. Thelilaments must substantially maintain their individual identitythroughout their length and must be bonded weakly enough so as to formuniform granules when severed.

' It is a comparatively easy matter in the present process to adjust thecooling liquid temperature, thegathering force, and the contact timewith the cooling liquid, before and after gathering, to produce a ribbonof adhering fila? ments with the characteristics above specified.

The accompanying drawing is a flow sheet illustrating the process of theinvention. Figure 1 is a side view of suitable apparatus,diagrammatically` illustrated. Figure 2 is a top view of the sameapparatus.

In the operation of the process illustrated in the drawing moltenpolymer is extruded from reactor 1 through the orifices 2 in the die 3.A single row of orifices form? ing one bank of filaments can be used butin preferred operations in accordance with the present process two orthree rows of orifices are used.

The filaments 4 enter cooling bath 5, suitably passing around guide bar6 which is set at a point where the filament surface has been cooledbelow the weld temperature.

From guide bar 6 the filaments travel through the cooling bath to thegathering rod 7 which suitably has the form of a doorway or inverted U.The position of gathering rod 7 is adjustable along the length of thecooling bath, and the separation between its vertical side bars 8 isadjustable. Top and bottom pressure on the ribbon of filaments as theyare gathered is adjustable by raising and lowering guide bar 9, which isassociated with gathering rod 7 a short distance away in the line ofmovement of the filaments. lt is shown as following the gathering rod,but it can also precede the gathering rod.

The filaments travel through the cooling liquid until they aresolidified into a connected ribbon structure. yIn the drawing the pathof travel through the liquid includes a chute 1l which can be movedlengthwise of the cooling bath to vary the length of travel of thefilaments through the cooling liquid after the gathering point.Alternatively a guide bar beyond the gathering rod, similar to guide bar6, can be used to fix lthe length of travel of the ribbon 12 of gatheredfilaments in the cooling liquid after the gathering point.

The solidified ribbon passes through feed rolls 13 into cutter 14, whichis a conventional cutter such as a rotary cutter. The stroke of thecutter slices across the advancing end of the ribbon and cuts a stripwhich falls into granules under the force of the cutting stroke.

- Any granules which remain adhering together can easilyv be separated,when operation isuproperly controlled as outlined below, by a shorttumbling or whirling or like operation. v

The operation of the presentprocess vcan very easily be controlled,since an `easily adjusted variable of domi nant influence is the time ofcontact `with the bath before the gathering point, i. e. the time whichcan be called the quench time. Under proper operation the ends of theindividual rods formingrthe connected ribbon drop oi largely or entirelyseparate, as granules, when the ribbon is cut. In the event that aconsiderable proportion of these ends adhere together after cutting, alonger quench time Ais given. by moving the gathering rod further fromthe extrusion die, while maintaining the same extrusiontemperaturefextrusion rate,` and cooling bath temperature as before.This adjustment is chective; it is not, however, unduly delicate and canusually be left unchanged even though there may be minor variations inoperating conditions.

Conversely, if the quench time is too long, individual filaments willbecome separated from `the ribbon structure aheadof` the feed rollsaforthel cutter; and will-jtend to buckle and cross over, producingirregular feed or jamming the feed rolls. This condition calls forshorter quench time, which is given by moving the gathering rod nearerto the extrusion die. With the bath Awater atfordinary cold watertemperatures of about i-25 C., the quench time will usually be aboutvl-2Y seconds.

The gathering pressure exerted laterally must be sutilcient to bringthe,A extruded: filamentsV into a ribbon. This ribbon can consist of aYsinglebank of filaments but preferably will be two or three; banksthick. The number of banks is fixed bysetting thexwidth of the gatheringrod equal to the width of ribbon. which will' be formed when theextruded iilaments are in light side-byfside contact in the desirednumber of banks. As take up speeds to the cutter increase, there will bea tendency to attenuate the filaments as they issue, in fused or plasticcondition, from the die, reducing their diameters and the widthof theribbon formed. This can be compensated by increasing extrusion pressuresto the point where the filaments come through the die atthe desireddiameter and .travel smoothly, without piling up below the extrusiondie.

The following are specific examples illustrative of the present process,butv the herein claimed invention is not to be understood as limited tothe details of the examples.

Example 1.-Molten molecularly orientable polycaprolactum under carbondioxide pressure of 17 p. s. i. gauge was extruded as round filaments ofrods ldownward into a water bath from a horizontal cylindrical dietransverse to the water bath, having along its down side a row ofSil-round orifices, the holes being aboubygg inch in diameter and about1A inch apart. Two andi-three rows of holes instead of only one row canbe used, giving increased production and generally better handling goingthrough the cutter. The holes suitably number 2575 per row.Advantageously, to prevent filaments from clinging to the die, `theorifices can be `given the external form of pyramids say i6 inch high.These im provements are illustrated .in Example 2 below.

The water bath tank had anoverffow pipe at the near end and a feed chuteat the-far end from-the extrusion die.

' The temperature of the molten-polycaprolactam was about 250 C. Thelsurface-of the Wat-er coolingbath was about 1/2 inch below the dieface. The Atemperature of'the water entering the bath was about 15 C.and the temperature of the water bath was about 20- C. The iirst guidebar contacted by the filaments was about 8 inches below the surface ofthe water in thel cooling bath, at which point the filament surfaces hadbeensuperiicially hardened,by cooling below the Weld temperature ofabout 215 C.

' The gathering rod wasY located 22 inches from-the first yguide rod'.The average' temperature ofthe filaments Ypassing under the gatheringrod was about 200 C. The

ing rod was about one inch farther along the coolingv bath than thegathering rod and was placed slightly higher than the top of thegathering rod whereby a flat ribbon of filaments was formed.

The ribbon of filaments passed out of the cooling bath and up ahuteabout 15- feet long at a speed of travel of.78 feetperminute to thefeed-rolls; thus the-quench time,A betweeny extrusionvand gathering,wasV about 2 seconds. ,v All filaments Aransmoothly and evenly, as anintegral ribbon through the feed rolls into a conventional rotary lknifecutter rotating at 1080 R. P, M.

The slicing strokes of the knives upon the end of the ribbon passingoverthe cutting block of the cutter formed cylindrical pellets of aboutly inch diameter and about 176,6 inch long. These pellets or granuleswere free owing', very uniform,.and substantially free of fines. Mostwere completely separate. A short whirling operation separatedsubstantially all of the granules one from another.

The laterall separation between the vertical side bars of the gatheringrod was adjusted t-o bring all the filaments into light side-by-sidecontact in one ribbon. The distance between the first guide bar and thegathering rod was adjusted relative to the temperature of the coolingbath and the speed of travel of the filaments so that theemerging-iilament--ribbon maintained its integrity. going through thefeed rollers While all filaments substantially maintained theirindividual identity throughout the length of the ribbon, rather thanforming a corrugated sheet. The lateral adhesion of one filament to thenext in the ribbon approaching the feed rolls was interrupted at randomintervals but all filaments were laterally joined in one integral ribbonstructure. The lateral bonds between filaments in the ribbon approachingthe feed rolls could be broken by a sudden twist such as produced bythe.slicing,action .ofl blades in a rotary cutter setfata smallVerticalangle such as 1 to the transverse line across the ribbon oflaments, whereby the filaments are cut sequentially rather thansimultaneously.

Example 2.-Using the apparatus described in Example l, moltenmolecularly orientable polycaprolactam under carbon dioxide pressure of35 p. s. i. gauge Was extruded from` a horizontal rectangular dietransverse to the ,water bath. This die had on its lower face two rowseach with 25 round orificesof pyramidal external form. The holes were 1Ainchin diameter, and 1A; inch apart.

' The extrudedfilaments or rods, somewhat attenuated as they moved awayfrom the die, passed downward and under a guide bar approximately 8inches below the surface of the cooling water. At this point somefilaments were moving together in 2 banks but most were spread out, moreor less at random, in a single bank. The gathering rod located 16 inchesfrom the guide bar gathered the laments into a ribbon 5 inches in width.It cooperated with a horizontal bar placed 3 inchesbeyond the gatheringrod and slightly higher than the top bar thereof, to bring the filamentsinto a Zabank ribbon as they passed under the gathering bar and over thehorizontal bar. Speed of travel of the ribbon was l5() feet per lminute. rlhel quench time, between. extrusion and gathering ofthefilaments, was accordingly about l second.

'The ribbon,.whichwas like that of Example l except for` being 2- banksthick,was fed by rolls into a conventional rotary knife cutter rotatingat 1300 R. P. M. This cutting followed by a short tumbling operationproduced separate cylindrical granules like those of Example 1, about0.1 inch long and 0.2 inch in diameter.

Dimensions of the apparatus and values of other variables given in theexamples can -be varied within reasonable ranges. For instance, thedistance between the orifices can be from about 1/{32 inch to about 1/2inch; and the extrusion rate of the filaments can vary over a range suchas feet per minute up to 200 feet per minute and faster. The practicalupper limitation on extrusion rate is the take-up speed of availablecutters.

When polycaprolactam is the polymer which is being granulated, theextrusion temperature should be at least about 210 C. and can be as highas about 300 C. A preferred range is about 225 275 C. The cooling watertemperature can be from freezing to about 90 C. The temperature of thecontacting surfaces of the polycaprolactam filaments at the gatheringrod must be below the weld temperature of about 215-225 C.

The average filament temperature must be in the plastic range in orderto form a ribbon of filaments held together by weak lateral bonds whileessentially preserving the individual identity of all filaments. Ingeneral this means that the average temperature of the filaments whengathered should be below but within 50 C. of the fusion temperature. Anaverage filament temperature during gathering not above the weldtemperature is desirable since -such average temperature assures thatthe contacting filament surfaces will be generally below the weldtemperature. Preferably the average filament temperature duringgathering is in the range between about 190 C. and about 210 C. forpolycaprolactam polymer.

The invention claimed is:

1. Process for forming granules from fusible, molecularly orientablethermoplastic organic polymer which comprises extruding from a melt ofsaid polymer separate, rounded, essentially uniform, essentiallynonmolecularlyoriented filaments; passing said filaments into an inertcooling liquid; cooling said filaments to surface temperature below thetemperature at which fusion occurs and coalescence between filamentswill develop immediately at all adjacent areas but with averagetemperature remaining in the range in which the filaments adhere whilemaintaining their individual identity; then immediately gatherings saidfilaments into side-by-side contact in a ribbon wherein each filamentsubstantially maintains its individual identity throughout its length;continuing to eX- tract heat from the surface of the ribbon except thelaterally contacting surfaces of the filaments, at a rate to allow theribbon to solidify into a connected structure; then passing the ribbonunder nonorienting tension to a cutter which severs the free end thereofand breaks the severed strip into separate granules at the lateral bondsybetween filament ends.

2. Process as defined in claim l wherein polycaprolactam is the polymeremployed; extrusion is at a temperature in the range between-about 210C. and about 300 C.; the cooling liquid is water at about 0-90 C.; andthe filaments are gathered after a quench time of about 1-2 secondsbetween extrusion and gathering.

3. Process as defined in claim 2 wherein the filaments are extruded from2 banks of holes spaced about J/32-1/2 inch apart; the filaments aregathered into a ribbon 2 banks thick; and the average temperature of thefilaments when gathered is about 200 C.

4. Process as defined in claim 2 wherein cooling liquid temperature,gathering force, and contact time with the cooling liquid areinteradjusted so that the lateral adhesion of one filament to the nextin the ribbon approaching the feed rolls is interrupted at randomintervals but al1 filaments are laterally joined in one integral ribbonstructure.

References Cited in the file of this patent UNITED STATES PATENTS2,464,746 Gering Mar. 15, 1949 2,746,086 Vickers May 22, 1956 FOREIGNPATENTS 1,079,945 France May 26, 1954 1,082,272 France June 16, 1954733,720 Great Britain July 20, 1955

1. PROCESS FOR FORMING GRANULES FROM FUSIBLE, MOLECULARLY ORIENTABLETHERMOPLASTIC ORGANIC POLYMER WHICH COMPRISES EXTRUDING FROM A MELT OFSAID POLYMER SEPARATE, ROUNDED, ESSENTIALLY UNIFORM, ESSENTIALLYNONMOLECULARLYORIENTED FILAMENTS; PASSING SAID FILAMENTS INTO AN INERTCOOLING LIQUID; COOLING SAID FILAMENTS TO SURFACE TEMPERATURE BELOW THETEMPERATURE AT WHICH FUSION OCCURS AND COALESCENCE BETWEEN FILAMENTSWILL DEVELOP IMMEDIATELY AT ALL ADJACENT AREAS BUT WITH AVERAGETEMPERATURE REMAINING IN THE RANGE IN WHICH THE FILAMENTS ADHERE WHILEMAINTAINING THEIR INDIVIDUAL IDENTITY; THEN IMMEDIATELY GATHERINGS SAIDFILAMENTS INTO SIDE-BY-SIDE CONTACT IN A RIBBON WHEREIN EACH FILAMENTSUBSTANTIALLY MAINTAINS ITS INDIVIDUAL IDENTITY THROUGHOUT ITS LENGTH;CONTINUING TO EXTRACT HEAT FROM THE SURFACE OF THE RIBBON EXCEPT THELATERALLY CONTACTING SURFACES OF THE FILAMENTS, AT A RATE TO ALLOW THERIBBON TO SOLIDIFY INTO A CONNECTED STRUCTURE; THEN PASSING THE RIBBONUNDER NONORIENTING TENSION TO A CUTTER WHICH SEVERS THE FREE END THEREOFAND BREAKS THE SEVERED STRIP INTO SEPARATE GRANULES AT THE LATERAL BONDSBETWEEN FILAMENT ENDS.